At least eight atrial peptides with potent renal, cardiovascular and endocrine effects have recently been isolated and sequenced from the atria of several species. The specific peptide that is released into the circulation is 28 amino acids in length but the role of these peptides in the regulation of fluid and electrolyte balance and cardiovascular function is unclear. This application proposes to test the hypothesis that atrial peptides participate in the regulation of fluid and electrolyte balance by reducing the sensitivity of the barorecptor reflexes and therefore reducing the control of cardiovascular and endocrine functions in dogs. Specifically, we will test the effect of atrial peptide infusions on the cardiac, vascular, vasopressin and ACTH responses to stimuli mimicking changes in blood pressure and volume. We will test the effect of atrial peptides on the reflex control of these variables when the high pressure, sino-aortic and low pressure, cardio-pulmonary receptors are stimulated individually and in combination. In addition, to determine if atrial peptides inhibit baroreceptor reflexes through direct effects on the central nervous system we will test the effect of atrial peptide infusion on the neuroendocrine responses to stimuli which directly stimulate vasopressin and ACTH secretion through effects on the hypothalamus and pituitary gland.